A horizontal stabiliser or tailplane assembly, as it is also known, is an example of an application that utilises a dual load path fastener system. The horizontal stabiliser comprises a fixed member and a hinged aft elevator. The arrangement of the hinged aft elevator relative to the fixed member is that of a joint, which is secured by a dual load path connector which facilitates pivotal movement of the elevator relative to the fixed member of the tailplane assembly.
The fastener arrangement is typically provided by an inner fastener/pin and an outer fastener/pin, where the outer pin is configured as a sleeve to receive the inner pin. Both pins are secured relative to each other such that they define separate and independent load paths. Therefore, if one pin fails the other pin provides a load path that can independently carry any load such that continued safe flight and landing is possible.
Federal Aviation regulations (FAR 25) requires, in respect of fasteners for a locking arrangement such as the dual load path fastener arrangement described above, that the fasteners are provided with a primary friction lock and a secondary mechanical locking device operable to lock the primary friction lock. A primary friction lock may be provided by, for example, a nut secured to a threaded shank.
An example of an existing locking arrangement for a dual load path fastener arrangement is that of a castellated nut providing the primary friction lock and a cotter pin as the mechanical locking device.
Typically, a hole is provided through the shank of the inner and outer pins in the region of a notch between castellations where the nut is fitted to the outer pin. When assembled the hole is aligned with a notch on the castellated nut and the cotter pin extends through the hole via the notch. By securing the cotter pin, in place, rotation of the castellated nut is prevented.
In the event that the outer pin fails it represents a redundant load and the pin is able to spin freely. Such free rotation can lead to shearing of the cotter pin, which may fall out and the continued free spinning of the outer pin may lead to loosening and ultimately removal of the castellated nut, which relies on friction to keep it secure. As such the arrangement does not represent a reliable fail-safe system.
It is desirable to provide an improved dual load path system.
It is further desirable to provide a dual load path system that mitigates the above problems.